PNS (tutorial)

Question 1

What is the PNS comprised of?

Answer 1

DRG - Dorsal Root Ganglion (the connection between the spinal cord and the muscles / sensory receptors)

Nerves + ganglia (outside of the brain and spinal cord)

Question 2

What signal / information comes into the dorsal root of the spinal cord?

And what signal / information comes into the ventral?

Answer 2

Sensory

Motor

Question 3

What is the plexus?

Answer 3

Spinal nerves

Question 4

What are the 5 major plexuses?

Answer 4

Cervical

Brachial

Lumbar

Sacral

Coccygeal

Question 5

How many nerves innervate to one part of the skin?

Answer 5

Many (not just one)

Question 6

What causes total sensory loss? Will cutting off one nerve that goes to that part of the body causes total sensory loss?

Answer 6

Cut off all nerves that innervate to that area to lose total sensation

No

Question 7

What is a dermatome?

Answer 7

An area of skin that is supplied by a single spinal nerve

Question 8

What happens if the dorsal root muscles are cut off?

Answer 8

Muscle weakness, sometimes eventually losing total muscle movement

Question 9

Which of the plexuses is more protected and least likely to be affected?

Answer 9

Lumbar-sacral plexus

Question 10

Where do the nerves that go in from L5 - S1 innervate from?

Answer 10

Big toe / feet

Question 11

How to test for lumbar discopathy?

Answer 11

Stretch raise test

Ask patient to lie down, stretch out leg and raise it - see if they get any pain

Question 12

Can the PNS regenerate?

Answer 12

Yes to a certain extent

Question 13

Why is decompression surgery then useful / effective?

Answer 13

Nerves after decompression can get better

Question 14

Name the labels A-D on this diagram:

Answer 14

A = Dorsal Root
B = Dorsal Root Ganglion
C = Plexus (spinal nerves)
D = Ventral Root

Question 15

What are the consequences if there were lesions at V-Z?

Suggest common medical scenarios which might result in a lesion occurring at each point.

Answer 15

V - sensation loss

W - Muscle weakness (not total loss of motor function)

X - Similar effects as cutting off at V and W, as it is cutting off at the part where those 2 roots merge?

Y - Loss of sensation from the muscle?

Z - Loss of motor function to the muscle

Strain injury
Prolapse disc - V and W lesions (causes loss of sensation or muscle weakness)
Trauma, peripheral neuropathy - Y and Z lesions
Lumbar plexus least likely to be affected

Question 16

50M - Has pain in his right leg. He reports that it extends from his buttock, down his thigh, calf and into his toes and that it gets worse when he moves. He describes the pain as stabbing, burning or shooting and has pins and needles in his right leg. He says that he feels as though his right leg is weaker than the left.

1. Which structures are involved to produce the symptoms?
2. What is the name of the condition?
3. What could be the cause of the condition?
4. What treatment options are available?

Answer 16

1. A mixture of the lumbar and sacral plexus - L5 and S1 (gluteus maximus? thigh)
   Innervates to the feet and big toe
2. Lumbar-spinal radiculopathy
3. Nerve compression (sciatic nerve)
   Slip disc
   Trauma to the disc
   Trauma to the bones = crush your nerves e.g. bone cancer
   Arthritis
   Piriformis syndrome - muscle that attaches the femur to the top of the pelvis can trap the nerve and compress it
4. Stretch-raise test can be used to diagnose - if they feel any pain while laying down, stretching out their leg and trying to raise it
   Physiotherapy, ibuprofen (if the pain it too high), injections i.e. epidural to the sacral portion, decompression surgery - discectomy (replacing the disc and clearing the compression)